Traditional passenger electric vehicles generally do not generate much heat when being driven around due to a lower average current. As the current is relatively low, the generated heat can be dissipated to the air via natural convection. Fast charging standards are increasing the amount of sustained current on all high voltage components. These fast charging currents generate significantly more heat than typical driving usage.
Currently, components such as contactors typically use connected busbars to draw away the heat. This heat is then released via natural convection. It is common, however, for junction boxes to have more than one contactor. This compounds the problem as more heat is being generated in smaller spaces.